The hydraulic actuator is used in machine tools and for other industrial uses in general as well as in driving devices of suction and exhaust valves of internal combustion engines. As the valves governing the suction and exhaust of the internal combustion engine have been driven by a crank shaft in the prior system, it has not been possible to freely control the timing and degree of opening of suction and exhaust valves.
LPG and CNG (compression natural gas) engines on which much expectation has been entertained as alternative engines in recent years suffer from strong knockings especially while they are running at a high speed. In order to solve this problem, the method of controlling freely the compression pressure of engine piston is effective, and in order to realize this, a mechanism of freely controlling electrically the opening/closing timing of the suction valve is necessary. The adoption of this mechanism enables even ordinary gasoline engines and Diesel engines to improve suction efficiency and fuel efficiency in a wide range of rotation speed. In addition, in the case of low speed and that of high speed, it becomes necessary to change the opening are of the valve and to change combustion performance. In this case, it becomes necessary to make the valve lift variable.
Some of recent high performance engines change the opening and closing timing of valves by advancing or retarding the angle of cam shaft or by changing the aperture of valve by switching between two types of cam for the valve, one for low speed and the other for high speed. In this case, however, only stepped control is possible. And as valve for cam-less engine, electromagnetic valves or valves combining electromagnetic type and hydraulic type have been proposed. However, these types tend to be excessively large or heavy and are not so practical (see for example Patent Documents 1 and 2).
Furthermore, as a cam-less and relatively small and light system, an electric hydraulic servo mechanism for the valve of internal combustion engine wherein a hydraulic servo mechanism having a larger operating power is put into action by electric signals is proposed (see for example Patent Document 3 and Non-Patent Document 1).
An example of the structure of a valve driving device disclosed in FIG. 1 of the Patent Document 3 is shown in FIG. 11. However, part numbers shown in FIG. 11 are partially changed from those shown in the Patent Document 3. The devices shown in FIG. 11 work as described below according to the description of the Patent Document 3.
Specifically, “the engine lubricating oil contained in the engine lubricating oil reservoir 12 placed within the engine is pressurized by a hydraulic pump 11 to be sent to the head of the suction and exhaust valve 1a. The hydraulic piston 2a at the head of the suction and exhaust valve 1a is put into action by the action of each electromagnetic solenoid 14 to open and close the suction and exhaust valve 1a. The opening and closing timing and the opening and closing time of the suction and exhaust valve 1a are determined as described in Table 1 of the Patent Document 3 based on the comprehensive judgment by the control computer for the opening and closing device of the suction and exhaust valve 6a of the signals received from various sensors 7a of the engine on the basic conditions such as engine speed, throttle opening, load and the like and the signals from the control computer for fuel control 8a used in the present engine and the hydraulic pressure is opened and closed by the electromagnetic solenoid 14.” Incidentally, in FIG. 11, 3a represents a hydraulic control valve, 5a represents a power battery, 9a represents an accumulator for accumulating hydraulic pressure, 10a represents a relief valve for setting pressure, and 13 represents a control relay.
The electro-hydraulic servomechanism for valves described in the Non-Patent Document 1 has been proposed by the inventor of the present patent application, and adopts a structure consisting of a hydraulic piston, a two-stage servo-valve (nozzle flap valve and spool valve), a displacement meter for measuring electrically the position of the piston.
Incidentally, the prior electro-hydraulic servomechanisms for valves described in the Patent Document 3 and the Non-Patent Document 1 involved the following problems in their actual use.
In the case of the prior devices, for example in the case of the device described in the Non-Patent Document 1, due to the use of a simple hydraulic piston, the mounting of a displacement meter for electric position sensors and the use of the servo-valve (two-stage type, nozzle flap valve and spool valve) with a low motive power efficiency of 33% at the maximum for control, the power consumption of the servomechanism is large, and due to a limit in responsiveness, the whole device was able to cope with an engine speed of approximately 2,000 rpm. Furthermore, electric sensors were problematic because of strong vibrations and reliability of their operation at a high temperature, and these problems constituted a bottleneck for their actual use.
In addition, in the opening and closing control of the valve of internal combustion engines, it is desirable that mechanical shocks be reduced to the minimum at the time of closing the valve from the viewpoint of vibration and life. In other words, a smooth landing control is required for reducing the landing velocity of the valve
[Patent Document 1]
Japanese Patent Application Laid Open 1995-34833 (p 3–5, FIG. 1)
[Patent Document 2]
Japanese Patent Application Laid Open 1999-511828 (p 11–12, FIGS. 5, 6)
[Patent Document 3]
Japanese Patent Application Laid Open 1999-173125 (p 2–4, FIGS. 1, 2)
[Non-Patent Document 1]
Hirohisa Tanaka: “Digital control and application of hydraulics and pneumatics,” published by Kindai Tosho K.K. on Oct. 25, 1987, p. 83–84.
The present invention was realized in view of the issues mentioned above, and the object of the present invention is to provide a cam-less and sensor-less variable valve system of internal combustion engine and a hydraulic actuator that enable to reduce power consumption, improve response speed and control smoothly landing speed.